The present invention relates to coke ovens generally and, more particularly, to the recovery of naphthalene from coke oven by-product gas.
In a conventional light oil recovery plant, the oil condensate from the vapor to oil heat exchanger (primary light oil) is usually returned to the benzolized wash oil stream of the wash oil still. This minimizes the loss of wash oil and does not normally cause a significant increase in the naphthalene concentration in the debenzolized wash oil.
Such practice is carried out in plants in which a naphthalene scrubber or oil type final cooler is used in conjunction with the light oil plant. Frequently, an additional rectifying section is added to the still which strips only the naphthalene rich oil from the naphthalene scrubber or oil type final cooler with the total vapors from the wash oil still. Such practice greatly improves the removal of naphthalene.
The method of operation normally recovers about three times the amount of naphthalene removed in a conventional light oil recovery plant. For this reason, the wash oil condensed in the vapor to oil heat exchanger, which is in equilibrium with the vapor leaving the heat exchanger, contains approximately three times the concentration of naphthalene which this condensate from conventional equipment would contain. Calculations indicate a concentration of 15 to 18% naphthalene in this condensed wash oil. Even though the amount of this condensed wash oil is small, calculations indicate that the concentration of naphthalene in the debenzolized oil is increased approximately 0.4%. This value can be even higher if there is a significant mechanical carry-over from the wash oil still. This higher concentration of naphthalene in the debenzolized wash oil means a higher concentration of naphthalene in the debenzolized gas, with attendant problems due to plugging of the subsequent piping and equipment.
How the method of the present invention minimizes the naphthalene content of the debenzolized gas will be evident to those skilled in the art from the following description and drawing.